An organic electroluminescence device (hereinafter the term “electroluminescence” is often abbreviated as “EL”) is a self-emission device utilizing the principle that a fluorescent substance emits light by the recombination energy of holes injected from an anode and electrons injected from a cathode when an electric field is impressed.
As the stack structure of the organic EL device, a two-layered type of a hole-transporting (injecting) layer and an electron-transporting emitting layer, a three-layered type of a hole-transporting (injecting) layer, an emitting layer and an electron-transporting (injecting) layer, or the like, are widely known. In such stack structure devices, their device structures and fabrication methods have been contrived to increase recombination efficiency of injected holes and electrons.
As the hole-transporting material used in an organic EL device, aromatic diamine derivatives or aromatic condensed ring diamine derivatives have heretofore been known.
However, in the case of an organic EL device using these aromatic diamine derivatives as the hole-transporting material, since an increased applied voltage is required to obtain sufficient luminance, problems such as a shortened device life or increased power consumption occur.
In order to solve the above-mentioned problems, doping of an electron-accepting compound such as a Lewis acid to a hole-injecting layer of an organic EL device has been proposed (Patent Documents 1 to 4 or the like). However, the electron-accepting compounds used in Patent Documents 1 to 4 have problems that they are unstable in handling during the production of an organic EL device, they shorten the life of an organic EL device due to the lack of stability such as heat resistance during driving of the organic EL device, or the like.
Tetrafluorotetracyanoquinodimethane (TCNQF4) exemplified as an electron-accepting compound in Patent Documents 3, 4 or the like has a high sublimation property since it has a small molecular weight and is substituted with fluorine. Therefore, when an organic EL device is fabricated by vacuum vapor deposition using this compound, the compound may diffuse within a deposition apparatus, and contaminate the apparatus and the device.    Patent Document 1: JP-A-2003-031365    Patent Document 2: JP-A-2001-297883    Patent Document 3: JP-T-2004-514257    Patent Document 4: US2005/0255334A1
The invention has been made in view of the above-mentioned problem, and an object thereof is to provide an electron-accepting material suitable for use as a constitution material of an organic EL device.